Enhancement: Update phpstan/phpstan and friends

[localheinz]

This PR

• updates phpstan/phpstan and friends
• fixes issues reported via static analysis

[codecov]

Codecov Report

Merging #101 into master will decrease coverage by 1.44%.
The diff coverage is 50%.

@@             Coverage Diff              @@
##             master     #101      +/-   ##
============================================
- Coverage       100%   98.55%   -1.45%     
- Complexity       47       48       +1     
============================================
  Files             5        6       +1     
  Lines           134      138       +4     
============================================
+ Hits            134      136       +2     
- Misses            0        2       +2

Impacted Files	Coverage Δ	Complexity Δ
src/Exception/MultipleDefinitionsFound.php	100% <ø> (ø)	2 <0> (ø)	⬇️
src/Construct.php	100% <ø> (ø)	7 <0> (ø)	⬇️
src/Constructs.php	97.77% <0%> (-2.23%)	34 <0> (ø)
src/Exception/ShouldNotHappen.php	100% <100%> (ø)	1 <1> (?)

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